The present invention relates to an improved process for the manufacture of 2-ethylhexyl acrylate by a direct esterification of acrylic acid with 2-ethylhexanol, this reaction being catalysed by sulphuric acid.
In this industrial process, to shift the reaction equilibrium, a solvent which azeotropically entrains the water of reaction is not added but this role is provided by an excess of the esterifying alcohol (in this instance, 2-ethylhexanol), which exhibits the distinguishing feature of forming an azeotrope with water.
On conclusion of the reaction stage, which is carried out batchwise, virtually all the sulphuric acid has been converted into 2-ethylhexyl hydrogensulphate (2-EtHexSO4H), according to the following reaction for the esterification of sulphuric acid with 2-ethylhexanol:
2-EtHexOH+H2SO4xe2x86x922-EtHexSO4H+H2O
Consequently, the reaction mixture, at the end of the reaction, comprises 2-ethylhexyl acrylate, 2-ethylhexanol, acrylic acid, 2-ethylhexyl hydrogensulphate, traces of sulphuric acid, and the stabilizers conventionally used in the reaction.
In the conventional process, the esterification reaction is followed by purification stages, generally carried out continuously:
the acidic entities present in the crude reaction mixture are neutralized by addition to the latter of an aqueous solution of a base (sodium hydroxide); during this stage, the acrylic acid is neutralized to sodium acrylate, the 2-ethylhexyl hydrogensulphate to neutral 2-ethylhexyl sulphate 2-EtHexSO4Na, and the traces of sulphuric acid to sodium sulphate Na2SO4, all these salts passing into the aqueous phase;
the separated organic phase resulting from the neutralization is washed with water in an extraction column, in order to remove the traces of impurities, of sodium hydroxide and of salts, and then the washed 2-ethylhexyl acrylate is conveyed to a first distillation column which makes it possible to remove, at the top, the light products, which light products are recycled to the esterification reaction; the topped ester is subsequently conveyed to a second column, from where it emerges at the top, purified from the heavy products;
the 2-ethylhexanol, present:
in the separated aqueous phase resulting from the neutralization, which essentially comprises neutral 2-ethylhexyl sulphate, 2-ethylhexanol, sodium acrylate and traces of sodium sulphate,
in the aqueous phase resulting from the esterification reaction proper, and
in the aqueous phase resulting from the washing of the organic phase in the extraction column,
is recovered, this recovery of the 2-ethylhexanol being carried out in a distillation column fed at the top with the aqueous liquors to be treated, in which column the 2-ethylhexanol is entrained at the top and can be recycled to the esterification reaction, whereas the column bottom product constitutes the waste aqueous liquors, freed from the 2-ethylhexanol, which will be discharged to the biological treatment plant.
As the aqueous liquors thus discharged are highly polluted with organic matter (measured by the chemical oxygen demand (COD)) because of the presence of neutral 2-ethylhexyl sulphate and sodium acrylate, an improved process for the manufacture of 2-ethylhexyl acrylate has been developed, which process forms the subject-matter of European Patent Application EP-A-609 127.
As may be described with reference to FIG. 1 in the appended drawing, in accordance with this known process, the reaction mixture (b1) is, as in the conventional process, neutralized with a sodium hydroxide solution and, on conclusion of this neutralization, the mixture separates on settling into two phases: an aqueous phase (a1) and an organic phase (o1).
After addition of sulphuric acid to (a1), in order to obtain a molar ratio of the number of H+ equivalents in excess to the number of moles of 2-ethylhexyl hydrogensulphate at least equal to 1.5, the new mixture (a2) is introduced into a hydrolysis reactor RHYD and brought to a temperature of the order of 70-200xc2x0 C. for a time of the order of 1-5 hours. The mixture, after reaction, is neutralized to pH 8 with 8% NaOH. The resulting phase (a3) is sent continuously to a distillation column C1 for recovery of the 2-ethylhexanol at the top and concentration at the bottom of the exhausted aqueous liquors intended for the biological treatment.
After a further neutralization with NaOH, the separated organic phase (o1) is washed with water in an extraction column C2 in order to remove the traces of impurities, of sodium hydroxide and of salts. The aqueous phase (a4) resulting from the bottom of the extraction column C2 is sent to a distillation column C1.
The washed 2-ethylhexyl acrylate obtained at the top of the column C2 is sent to a first distillation column C3 which makes it possible to remove, at the top, the light products composed essentially of 2-ethylhexanol, which products are recycled to the esterification reaction. The topped 2-ethylhexyl acrylate, obtained at the bottom, is sent to the second distillation column C4, from where it exits at the top, purified from the heavy products.
During the implementation of this process for the manufacture of 2-ethylhexyl acrylate, it appears that a dense emulsion is formed at the interphase during the separation by settling which takes place subsequent to the abovementioned neutralization stage. This emulsion, which might be due to 2-ethylhexyl acrylate polymers growing at the interphase, disrupts the downstream distillation line and lowers the environmental performance of the manufacturing plant.
The stage of neutralization of the crude reaction mixture generates most of the COD of the plant due to the sodium acrylate, which originates, on the one hand, from the neutralization of the unconverted acrylic acid and, on the other hand, from the saponification of the 2-ethylhexyl acrylate.
The inventors have discovered that these problems can be solved without chemical treatment by the suppression of the neutralization with NaOH of the phases (b1) and (o1), the 2-ethylhexyl hydrogensulphate being removed by washing with water and separating by settling in the column C2, the residual acrylic acid not extracted into the aqueous phase as was the case in the known process according to EP-A-609 127, being removed at the top of the topping column C3.
A subject-matter of the present invention is therefore a process for the manufacture of 2-ethylhexyl acrylate by direct esterification of acrylic acid with 2-ethylhexanol in the presence of at least one stabilizer for acrylic acid, the said esterification being catalysed by sulphuric acid, the crude reaction mixture (B1) obtained comprising 2-ethylhexyl acrylate, 2-ethylhexanol, acrylic acid, 2-ethylhexyl hydrogensulphate, traces of sulphuric acid and the usual impurities, characterized in that the crude reaction mixture (B1) is washed with water in an extraction column C2 which makes it possible to obtain, at the top, an organic phase (O2) and to remove, at the bottom, an aqueous phase (A1),
the organic phase (O2) being sent to a topping column C3 which makes it possible to obtain, at the top, the acrylic acid and the 2-ethylhexanol present in the phase (O2), which products are recycled to the esterification reaction, the topped 2-ethylhexyl acrylate being sent to a second distillation column C4, from where it emerges at the top, purified from the heavy products; and
the aqueous phase (A1) being sent to a stage of hydrolysis of the 2-ethylhexyl hydrogensulphate present in the said aqueous phase (A1), the hydrolysis being carried out so as to form, in the said phase, 2-ethylhexanol and sulphuric acid, the acidic entities resulting from the said hydrolysis being neutralized by introduction of a base into the medium, and the resulting aqueous phase (A3) being sent to a stage of recovery of the 2-ethylhexanol in a distillation column C1, the said alcohol being entrained into the top of the said column C1.
In accordance with specific embodiments of the process according to the invention:
the washing of the crude reaction mixture (B1) with water is carried out with the use of 5 to 50% by weight of water with respect to the charge of crude reaction mixture (B1); furthermore, this stage of washing the crude reaction mixture (B1) with water is generally carried out at a temperature of 20-50xc2x0 C.; and
the hydrolysis is carried out at a temperature of between 70 and 200xc2x0 C.
To give a better illustration of the subject-matter of the present invention, an implementational example (Example 1) thereof will be described below with reference to FIG. 2 of the appended drawing, which represents the diagram of the process according to the invention. Comparative Example 2 is presented with reference to the abovementioned FIG. 1, which figure illustrates the known process. In the examples, the parts and percentages are by weight.
The progression of the various streams illustrated in FIGS. 1 and 2 has been described above.
The entire disclosure[s] of all applications, patents and publications, cited above or below, and of corresponding French Application No. 01.04442, filed Apr. 2, 2001 are hereby incorporated by reference.